1. Field of the Invention
The present invention relates to a display device and a display system which provide a unit for brightness adjustment in accordance with illuminance of an installation environment and contents of display images.
2. Description of the Background Art
In a conventional display device, a system which performs brightness adjustment of a display is configured as shown in FIG. 20. In FIG. 20, the system includes a liquid crystal panel 41, a backlight module 42 attached to the liquid crystal panel 41, an inverter circuit 43 connected to the backlight module 42, a power supply circuit 44 which supplies driving power to the inverter circuit 43 and a control circuit 45 whose output is connected to the inverter circuit 43. The backlight module 42 is composed of a plurality of cold cathode fluorescent lamps (CCFLs). The inverter circuit 43 drives the backlight module 42. The control circuit 45 controls a pulse width and a frequency of a driving waveform output to the inverter circuit 43, and controls power supplied from a power source to the inverter, to thereby control brightness of a screen.
Here, screen brightness is appropriately set by a user in accordance with input setting by an external communication unit such as a remote controller, a push button or the like, and a setting value thereof is stored in a nonvolatile memory inside a controller.
In this case, when illuminance around the display changes under use environment due to an effect of outside light or the like, eyes of a person are adapted to surrounding environment, which results in a decrease in visibility. In addition, when brightness is increased more than necessary, power is consumed uselessly.
As measures against the above-mentioned problems, there are a system which measures brightness around a display on a front side to automatically adjust brightness of a display (for example, see Japanese Patent Application Laid-Open No. 09-146073 (1997)), a system which measures an illuminance by a remote controller in addition to an illuminance of a liquid crystal display panel to use those illuminances for control (for example, see Japanese Patent Application Laid-Open No. 2006-72255), and a system which uses a plurality of sensors, which are installed around a screen, for control (for example, see Japanese Patent Application Laid-Open No. 2007-310096).
In the above-mentioned systems, illuminance sensors are provided on a display surface of the display or around the display surface, and there is provided a unit which directly measures light entering the display surface of the display or measures illuminance of a place apart from the display surface of the display. However, it is conceivable as shown in FIG. 21 that eyes of an actual user (observer) are adapted to light (background) which is caused to enter the display surface of the display from a direction with a rear surface of the display being as a center, not to light entering the display surface of the display.
Accordingly, in a case where sensors are installed on a display surface of a display, it may be difficult to perform accurate control adapted to a change of outside light in some cases.
For example, as shown in FIG. 22, in a case where large displays for information display are installed at a window of a building in a state of being suspended from a ceiling, eyes of an observer are adapted to outside light entering a display surface from the window, but are not necessarily adapted to a light source inside the building. In a case where a ratio of the display surface of the display with respect to a visual field of the observer is relatively small, that is, under most of installation environments of a display for public display, it is naturally considered that the eyes of the observer are not adapted to reflected light (generally, reflectance is 5% or less) of light entering the display surface of the display but adapted to reflected light on a wall behind the display, outside light from the window behind the display or the like (FIG. 21).
Therefore, there arises a problem that a conventional display device cannot accurately obtain an effect of ambient light and be adapted thereto.
Further, in a case where displays individually perform an operation of correcting outside light in a system in which a single large screen is formed using a plurality of display devices, there arises a problem that differences (variations) are caused in brightness control for displays due to variations in sensor for measuring outside light or differences in setting position.